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Versions: 00 01 02 03 04 05 rfc3016                                     
Internet Engineering Task Force                 Yoshihiro Kikuchi - Toshiba
Internet Draft                                       Toshiyuki Nomura - NEC
Document: draft-ietf-avt-rtp-mpeg4-es-02.txt         Shigeru Fukunaga - Oki
                                              Yoshinori Matsui - Matsushita
                                                       Hideaki Kimata - NTT
                                                               July 6, 2000


             RTP payload format for MPEG-4 Audio/Visual streams


Status of this Memo

   This document is an Internet-Draft and is in full conformance with all
      provisions of Section 10 of RFC2026 [1].

   Internet-Drafts are working documents of the Internet Engineering Task
   Force (IETF), its areas, and its working groups. Note that other groups
   may also distribute working documents as Internet-Drafts. Internet-Drafts
   are draft documents valid for a maximum of six months and may be updated,
   replaced, or obsoleted by other documents at any time. It is
   inappropriate to use Internet- Drafts as reference material or to cite
   them other than as "work in progress."
   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt
   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.






                                   Abstract

   This document describes RTP payload formats for carrying of MPEG-4 Audio
   and Visual bitstreams[2][3]. For the purpose of directly mapping MPEG-4
   Audio/Visual bitstreams onto RTP packets, it provides specifications for
   the use of RTP header fields and also specifies fragmentation rules. It
   also provides specifications for MIME type registrations and the use of
   SDP.













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RTP payload format for MPEG-4 Audio/Visual streams       February 2000


1. Introduction

   The RTP payload formats described in this Internet-Draft specify a way of
   how MPEG-4 Audio and Visual streams are to be fragmented and mapped
   directly onto RTP packets.

   These RTP payload formats enable to carry MPEG-4 Audio/Visual streams
   without using the synchronization and stream management functionality of
   MPEG-4 Systems [6]. Such RTP payload format would be used within systems
   where their own stream management functionality is provided and thus such
   functionality in MPEG-4 Systems is not necessary. H.323 terminals are an
   example of such systems. MPEG-4 Audio/Visual streams are not managed by
   MPEG-4 Systems Object Descriptors  but by H.245. The streams are directly
   mapped onto RTP packets without using the synchronization functionality
   of MPEG-4 Systems. Other examples are SIP and RTSP where attribute of the
   video stream (e.g. media type, packetization format and configuration) is
   specified in MIME and SDP parameters.

   The semantics of RTP headers in such cases need to be clearly defined,
   including the association with MPEG-4 Audio/Visual data elements.  In
   addition, it would be beneficial to define the fragmentation rules of RTP
   packets for MPEG-4 Video streams so as to enhance error resiliency by
   utilizing the error resilience tools provided inside the MPEG-4 Video
   stream.  These issues, however, have yet to be addressed by other RTP
   payload format specifications.


1.1 MPEG-4 Visual RTP payload format

   MPEG-4 Visual is a visual coding standard with many new features: high
   coding efficiency; high error resiliency; multiple, arbitrary shape
   object-based coding; etc. [2]. It covers a wide range of bitrate from
   scores of Kbps to several Mbps. It also covers a wide variety of
   networks, ranging from those guaranteed to be almost error-free to mobile
   networks with high error rates.

   With respect to the fragmentation rules for an MPEG-4 visual bitstream
   defined in this document, since MPEG-4 Visual is used for a wide variety
   of networks, it is desirable not to apply too much restriction on
   fragmentation, and a fragmentation rule such as "a single video packet
   shall always be mapped on a single RTP packet" may be inappropriate. On
   the other hand, careless, media unaware fragmentation may cause
   degradation in error resiliency and bandwidth efficiency. The
   fragmentation rules described in this document are flexible but manage to
   define the minimum rules for preventing meaningless fragmentation and for
   utilizing the error resilience of MPEG-4 visual.

   While the additional media specific RTP header defined for such video
   coding tools as H.261 or MPEG-1/2 is effective in helping to recover
   picture headers corrupted by packet losses, in MPEG-4 Visual there are
   already error resilience functionalities for recovering corrupt headers,
   and these can be used on RTP/IP networks, as well as on other networks.

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RTP payload format for MPEG-4 Audio/Visual streams       February 2000


   (H.223/mobile, MPEG-2/TS, etc.) That is why no extra RTP header fields
   are defined in the MPEG-4 Visual RTP payload format proposed here.


1.2 MPEG-4 Audio RTP payload format

   MPEG-4 Audio is a new kind of audio standard that integrates many
   different types of audio coding tools. It also supports a mechanism for
   representing synthesized sounds. Low-overhead MPEG-4 Audio Transport
   Multiplex (LATM) manages the sequences of audio data with relatively
   small overhead. In audio-only applications, then, it is desirable for
   LATM-based MPEG-4 Audio bitstreams to be directly mapped onto the RTP
   packets without using MPEG-4 Systems.

   For MPEG-4 Audio coding tools except synthesis tools, as is true for
   other audio coders, if the payload of a packet is a single audio frame,
   packet loss will not impair the decodability of adjacent packets.  On the
   other hands, MPEG-4 Audio synthesis tools may be sensitive to error. For
   example, an SA_access_unit in the payload may set a global value to a new
   value, which is then references throughout the audio content to make a
   macro change in the performance. In this case, an error in the payload
   influences all audio data produced after the error. In order to enhance
   error resiliency, the element of SA_access_unit that makes the above
   macro change should be transmitted across several SA_access_unit
   repeatedly. The number of repetition will be dependent on the network
   condition. Therefore, the additional media specific header for recovering
   errors will not be required for MPEG-4 Audio.




2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC-2119 [7].




3. RTP Packetization of MPEG-4 Visual bitstream

   This section specifies RTP packetization rules for MPEG-4 Visual content.
   An MPEG-4 Visual bitstream is mapped directly onto the RTP payload
   without any addition of extra header fields or any removal of Visual
   syntax elements. The Combined Configuration/Elementary stream mode is
   used so that configuration information will be carried to the same RTP
   port as the elementary stream. (see 6.2.1 "Start codes" of ISO/IEC 14496-
   2 [2][9][4]) The configuration information MAY additionally be specified
   by some out-of-band means; in H.323 terminals, H.245 codepoint
   "decoderConfigurationInformation" MAY be used for this purpose; in
   systems using MIME content type and SDP parameters, e.g. SIP and RTSP,

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RTP payload format for MPEG-4 Audio/Visual streams       February 2000


   the optional parameter "config" MAY be used to specify the configuration
   information. (see 5.1 and 5.2)

   When the short video header mode is used, the RTP payload format used MAY
   be that specified for H.263 in the relevant RFCs or in other relevant
   standards.















































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RTP payload format for MPEG-4 Audio/Visual streams       February 2000


   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |V=2|P|X|  CC   |M|     PT      |       sequence number         | RTP
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           timestamp                           | Header
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           synchronization source (SSRC) identifier            |
   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
   |            contributing source (CSRC) identifiers             |
   |                             ....                              |
   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
   |                                                               | RTP
   |       MPEG-4 Visual stream (byte aligned)                     | Payload
   |                                                               |
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               :...OPTIONAL RTP padding        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 1 - An RTP packet for MPEG-4 Visual stream




3.1 Use of RTP header fields for MPEG-4 Visual

   Payload Type (PT): Payload type is to be specifically assigned as the
   MPEG-4 Visual RTP payload format. If this assignment is to be carried out
   dynamically, it can be performed by such out-of-band means as H.245, SDP,
   etc.


   Extension (X) bit: Defined by the RTP profile used.


   Sequence Number: Incremented by one for each RTP data packet sent,
   starting, for security reasons, with a random initial value.


   Marker (M) bit: The marker bit is set to one to indicate the last RTP
   packet (or only RTP packet) of a VOP.


   Timestamp: The timestamp indicates the composition time, or the
   presentation time in a no-compositor decoder. A constant offset, which is
   random, is added for security reasons. For a video object plane, it is
   defined as vop_time_increment (in units of
   1/vop_time_increment_resolution seconds) plus the cumulative number of
   whole seconds specified by module_time_base and, if present, time_code of
   Group_of_VideoObjectPlane() fields.  In the case of interlaced video, a
   VOP will consist of lines from two fields, and the timestamp will
   indicate the composition time of the first field. If the RTP packet

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RTP payload format for MPEG-4 Audio/Visual streams       February 2000


   contains only configuration information and/or
   Group_of_VideoObjectPlane() fields, the composition time of the next VOP
   in the coding order is used. If the RTP packet contains only
   visual_object_sequence_end_code information, the composition time of the
   immediately preceding VOP in the coding order is used.

   The resolution of the timestamp is set to its default value of 90KHz,
   unless specified by an out-of-band means (e.g. SDP parameter or MIME
   parameter as defined in section 5).


   SSRC, CC and CSRC fields are used as described in RFC 1889 [8].


3.2 Fragmentation of MPEG-4 Visual bitstream

   A fragmented MPEG-4 Visual bitstream is mapped directly onto the RTP
   payload without any addition of extra header fields or any removal of
   Visual syntax elements. The Combined Configuration/Elementary streams
   mode is used. The following rules apply for the fragmentation.

   (1) Configuration information and Group_of_VideoObjectPlane() fields
   SHALL be placed at the beginning of the RTP payload (just after the RTP
   header) or just after the header of the syntactically upper layer
   function.

   (2) If one or more headers exist in the RTP payload, the RTP payload
   SHALL begin with the header of the syntactically highest function.
   Note: The visual_object_sequence_end_code is regarded as the lowest
   function.

   (3) A header SHALL NOT be split into a plurality of RTP packets.

   (4) Two or more VOPs SHALL be fragmented into different RTP packets so
   that one RTP packet consists of the data bytes associated with a unique
   presentation time (that is indicated in the timestamp field in the RTP
   packet header).

   (5) A single video packet SHOULD NOT be split into a plurality of RTP
   packets. The size of a video packet SHOULD be adjusted in such a way that
   the resulting RTP packet is not larger than the path-MTU. A video packet
   MAY be split into a plurality of RTP packets when the size of the video
   packet is large.
   (Rule (5) does not apply to the enhancement layer of the scalable streams
   where the video packet is not supported.)


   Here, header means:
   - Configuration information (Visual Object Sequence Header, Visual Object
     Header and Video Object Layer Header)
   - visual_object_sequence_end_code


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RTP payload format for MPEG-4 Audio/Visual streams       February 2000


   - The header of the entry point function for an elementary stream
     (Group_of_VideoObjectPlane() or the header of VideoObjectPlane(),
     video_plane_with_short_header(), MeshObject() or FaceObject())
   - The video packet header (video_packet_header() excluding
     next_resync_marker())
   - The header of gob_layer()
   See 6.2.1 "Start codes" of ISO/IEC 14496-2[2][9][4] for the definition of
   the configuration information and the entry point functions.


   The video packet starts with the VOP header or the video packet header,
   followed by motion_shape_texture(), and ends with next_resync_marker() or
   next_start_code().


3.3 Examples of packetized MPEG-4 Visual bitstream

   Considering the fact that MPEG-4 Visual covers a wide variety of networks
   ranging from scores of Kbps to several Mbps, and from those guaranteed to
   be almost error-free to mobile networks with high error rates, it is
   desirable not to apply too much restriction on fragmentation. On the
   other hand, careless, media unaware fragmentation will cause degradation
   in error resiliency and bandwidth efficiency. The fragmentation criteria
   described in 3.2 are flexible but to define the minimum rules to prevent
   meaningless fragmentation.


   Figure 2 shows examples of RTP packets generated based on the criteria
   described in 3.2

   (a) is an example of the first RTP packet or the random access point of
   an MPEG-4 visual bitstream containing the configuration information.
   According to criterion (1), the Visual Object Sequence Header(VS header)
   is placed at the beginning of the RTP payload, preceding the Visual
   Object Header and the Video Object Layer Header(VO header, VOL header).
   Since the fragmentation rule defined in 3.2 guarantees that the
   configuration information, starting with
   visual_object_sequence_start_code, is always placed at the beginning of
   the RTP payload, RTP receivers can detect the random access point by
   checking if the first 32-bit field of the RTP payload is
   visual_object_sequence_start_code.

   (b) is another example of the RTP packet containing the configuration
   information. It differs from example (a) in that the RTP packet also
   contains a video packet in the VOP following the configuration
   information. Since the length of the configuration information is
   relatively short (typically scores of bytes) and an RTP packet containing
   only the configuration information may thus increase the overhead, the
   configuration information and the immediately following GOV and/or (a
   part of) VOP can be effectively packetized into a single RTP packet as in
   this example.


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RTP payload format for MPEG-4 Audio/Visual streams       February 2000


   (c) is an example of the RTP packet that contains
   Group_of_VideoObjectPlane(GOV). Following criterion (1), the GOV is
   placed at the beginning of the RTP payload. It would be a waste of RTP/IP
   header overhead to generate an RTP packet containing only a GOV whose
   length is 7 bytes. Therefore, (a part of) the following VOP can be placed
   in the same RTP packet as shown in (c).

   (d) is an example of the case where one video packet is packetized into
   one RTP packet. When the packet-loss rate of the underlying network is
   high, this kind of packetization is recommended. It is recommended to set
   resync_marker_disable to 0 in the VOL header to enable the adjustment of
   the video packet size. Even when the RTP packet containing the VOP header
   is discarded by a packet loss, the other RTP packets can be decoded by
   using the HEC(Header Extension Code) information in the video packet
   header. No extra RTP header field is necessary.

   (e) is an example of the case where more than one video packets are
   packetized into one RTP packet. This kind of packetization is effective
   to save the overhead of RTP/IP headers when the bit-rate of the
   underlying network is low. However, it will decrease the packet-loss
   resiliency because multiple video packets are discarded by a single RTP
   packet loss. The optimal number of video packets in an RTP packet and the
   length of the RTP packet can be determined considering the packet-loss
   rate and the bit-rate of the underlying network.


   Figure 3 shows examples of RTP packets prohibited by the criteria of 3.2.

   Fragmentation of a header into multiple RTP packets, as in (a), will not
   only increase the overhead of RTP/IP headers but also decrease the error
   resiliency. Therefore, it is prohibited by the criterion (3).

   When concatenating more than one video packets into an RTP packet, VOP
   header or video_packet_header() shall not be placed in the middle of the
   RTP payload. The packetization as in (b) is not allowed by criterion (2)
   due to the aspect of the error resiliency. Comparing this example with
   Figure 2(d), although two video packets are mapped onto two RTP packets
   in both cases, the packet-loss resiliency is not identical. Namely, if
   the second RTP packet is lost, both video packets 1 and 2 are lost in the
   case of Figure 3(b) whereas only video packet 2 is lost in the case of
   Figure 2(d).

   An RTP packet containing more than one VOPs, as in (c), is not allowed.










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RTP payload format for MPEG-4 Audio/Visual streams       February 2000


       +------+------+------+------+
   (a) | RTP  |  VS  |  VO  | VOL  |
       |header|header|header|header|
       +------+------+------+------+

       +------+------+------+------+------------+
   (b) | RTP  |  VS  |  VO  | VOL  |Video Packet|
       |header|header|header|header|            |
       +------+------+------+------+------------+

       +------+-----+------------------+
   (c) | RTP  | GOV |Video Object Plane|
       |header|     |                  |
       +------+-----+------------------+

       +------+------+------------+  +------+------+------------+
   (d) | RTP  | VOP  |Video Packet|  | RTP  |  VP  |Video Packet|
       |header|header|    (1)     |  |header|header|    (2)     |
       +------+------+------------+  +------+------+------------+

       +------+------+------------+------+------------+------+------------+
   (e) | RTP  |  VP  |Video Packet|  VP  |Video Packet|  VP  |Video Packet|
       |header|header|     (1)    |header|    (2)     |header|    (3)     |
       +------+------+------------+------+------------+------+------------+

        Figure 2 - Examples of RTP packetized MPEG-4 Visual bitstream


       +------+-------------+  +------+------------+------------+
   (a) | RTP  |First half of|  | RTP  |Last half of|Video Packet|
       |header|  VP header  |  |header|  VP header |            |
       +------+-------------+  +------+------------+------------+

       +------+------+----------+  +------+---------+------+------------+
   (b) | RTP  | VOP  |First half|  | RTP  |Last half|  VP  |Video Packet|
       |header|header| of VP(1) |  |header| of VP(1)|header|    (2)     |
       +------+------+----------+  +------+---------+------+------------+

       +------+------+------------------+------+------------------+
   (c) | RTP  | VOP  |Video Object Plane| VOP  |Video Object Plane|
       |header|header|        (1)       |header|       (2)        |
       +------+------+------------------+------+------------------+

   Figure 3 - Examples of prohibited RTP packetization for MPEG-4 Visual
   bitstream








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RTP payload format for MPEG-4 Audio/Visual streams       February 2000


4. RTP Packetization of MPEG-4 Audio bitstream

   This section specifies RTP packetization rules for MPEG-4 Audio
   bitstreams. MPEG-4 Audio streams are formatted by LATM (Low-overhead
   MPEG-4 Audio Transport Multiplex) tool[5], and the LATM-based streams are
   then mapped onto RTP packets as described the three sections below.

4.1 RTP Packet Format

   LATM-based streams consist of a sequence of audioMuxElements that include
   one or more audio frames. A complete audioMuxElement or a part of one
   SHALL be mapped directly onto an RTP payload without any removal of
   audioMuxElement syntax elements (see Figure 4). The first byte of each
   audioMuxElement SHALL be located at the first payload location in an RTP
   packet.


   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |V=2|P|X|  CC   |M|     PT      |       sequence number         |RTP
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           timestamp                           |Header
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           synchronization source (SSRC) identifier            |
   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
   |            contributing source (CSRC) identifiers             |
   |                             ....                              |
   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
   |                                                               |RTP
   :                 audioMuxElement (byte aligned)                :Payload
   |                                                               |
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               :...OPTIONAL RTP padding        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                Figure 4 - An RTP packet for MPEG-4 Audio

   In order to decode the audioMuxElement, the following muxConfigPresent
   information is required to be indicated by an out-of-band means.

   muxConfigPresent: If this value is set to 1, the audioMuxElement SHALL
   include an indication bit "useSameStreamMux" and MAY include the
   configuration information for audio compression "StreamMuxConfig". The
   useSameStreamMux bit indicates whether the StreamMuxConfig element in the
   previous frame is applied in the current frame.

4.2 Use of RTP Header Fields for MPEG-4 Audio

   Payload Type (PT): Payload type is to be specifically assigned as the
   MPEG-4 Audio RTP payload format. If this assignment is to be carried out
   dynamically, it can be performed by such out-of-band means as H.245, SDP,
   etc.

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RTP payload format for MPEG-4 Audio/Visual streams       February 2000



   Marker (M) bit: The marker bit indicates audioMuxElement boundaries. It
   is set to one to indicate that the RTP packet contains a complete
   audioMuxElement or the last fragment of an audioMuxElement.

   Timestamp: The timestamp indicates composition time, or presentation time
   in a no-compositor decoder. Timestamps are recommended to start at a
   random value for security reasons.

   Unless specified by an out-of-band means, the resolution of the timestamp
   is set to its default value of 90 kHz.

   Sequence Number: Incremented by one for each RTP packet sent, starting,
   for security reasons, with a random value.

   SSRC, CC and CSRC fields are used as described in RFC 1889 [8].

4.3 Fragmentation of MPEG-4 Audio bitstream

   It is desirable to put one audioMuxElement in each RTP packet. If the
   size of an audioMuxElement can be kept small enough that the size of the
   RTP packet containing it does not exceed the size of the path-MTU, this
   will be no problem. If it cannot, the audioMuxElement MAY be fragmented
   and spread across multiple packets, following the rules below:

   (1) "payloadMux", which consists of payload elements, MAY be fragmented
   across several RTP packets, so that each of those RTP packets will
   contain one or more payload elements. Individual payload elements
   themselves SHOULD NOT be fragmented.

   (2) If the audioMuxElement includes StreamMuxConfig, StreamMuxConfig
   SHALL be included in the RTP packet that contains the first payload
   element.




5. MIME type registration for MPEG-4 Audio/Visual streams

   The following sections describe the MIME type registrations for MPEG-4
   Audio/Visual streams. MIME type registration and SDP usage for the MPEG-4
   Visual stream are described in Sections 5.1 and 5.2, respectively, while
   MIME type registration and SDP usage for MPEG-4 Audio stream are
   described in Sections 5.3 and 5.4, respectively.

   (In the following sections, the RFC number "XXXX" represents the RFC
   number, which should be assigned for this Internet Draft.)


5.1 MIME type registration for MPEG-4 Visual

   MIME media type name: video

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RTP payload format for MPEG-4 Audio/Visual streams       February 2000



   MIME subtype name: MP4V

   Required parameters: none

   Optional parameters:
     rate: This parameter is used only for RTP transport. It indicates the
     resolution of the timestamp field in the RTP header. If this parameter
     is not specified, its default value of 90000 (90KHz) is used.

     profile-level-id: A decimal representation of MPEG-4 Visual Profile
     Level indication value (profile_and_level_indication) defined in Table
     G-1 of ISO/IEC 14496-2 [2][4].

     config: A hexadecimal representation of an octet string that expresses
     the MPEG-4 Visual configuration information, as defined in subclause
     6.2.1 Start codes of ISO/IEC14496-2[2][4][9]. The configuration
     information is mapped onto the octet string in an MSB-first basis. The
     first bit of the configuration information SHALL be located at the MSB
     of the first octet. The configuration information indicated by this
     parameter SHALL be the same as the configuration information in the
     corresponding MPEG-4 Visual stream, except for
     first_half_vbv_occupancy and latter_half_vbv_occupancy, if exist,
     which may vary in the repeated configuration information inside an
     MPEG-4 Visual stream (See 6.2.1 Start codes of ISO/IEC14496-2).

     The parameter "profile-level-id" MAY be used in the capability
     exchange procedure to indicate MPEG-4 Visual Profile and Level
     combination of which the MPEG-4 Visual codec is capable. The parameter
     "config" MAY be used to indicate the configuration of the
     corresponding MPEG-4 visual bitstream, but SHALL NOT be used to
     indicate the codec capability in the capability exchange procedure.

     Example usages for these parameters are:
       - MPEG-4 Visual Simple Profile/Level 1:
          Content-type: video/mp4v; profile-level-id=1

       - MPEG-4 Visual Core Profile/Level 2:
          Content-type: video/mp4v; profile-level-id=34

       - MPEG-4 Visual Advanced Real Time Simple Profile/Level 1:
          Content-type: video/mp4v; profile-level-id=145


   Published specification:
     The specifications for MPEG-4 Visual streams are presented in ISO/IEC
     14469-2[2][4][9]. The RTP payload format is described in RFCXXXX.

   Encoding considerations:
     Video bitstreams must be generated according to MPEG-4 Visual
     specifications (ISO/IEC 14496-2). A video bitstream is binary data and
     must be encoded for non-binary transport (for Email, the Base64

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RTP payload format for MPEG-4 Audio/Visual streams       February 2000


     encoding is sufficient).  This type is also defined for transfer via
     RTP. The RTP packets MUST be packetized according to the MPEG-4 Visual
     RTP payload format defined in RFCXXXX.

   Security considerations:
     See section 6 of RFCXXXX.

   Interoperability considerations:
     MPEG-4 Visual provides a large and rich set of tools for the coding of
     visual objects. For effective implementation of the standard, subsets
     of the MPEG-4 Visual tool sets have been provided for use in specific
     applications. These subsets, called 'Profiles', limit the size of the
     tool set a decoder is required to implement. In order to restrict
     computational complexity, one or more Levels are set for each Profiles.
     A Profile@Level combination allows:

     o a codec builder to implement only the subset of the standard he
     needs, while maintaining interworking with other MPEG-4 devices
     included in the same combination, and

     o checking whether MPEG-4 devices comply with the standard
     ('conformance testing').

     The visual stream SHALL be compliant with the MPEG-4 Visual
     Profile@Level specified by the parameter "profile-level-id".
     Interoperability between a sender and a receiver may be achieved by
     specifying the parameter "profile-level-id" in MIME content, or by
     arranging in the capability exchange procedure to set this parameter
     mutually to the same value.


   Applications which use this media type:
     Audio and visual streaming and conferencing tools, Internet messaging
     and Email applications.

   Additional information: none

   Person & email address to contact for further information:
     The authors of RFCXXXX. (See section 8)

   Intended usage: COMMON

   Author/Change controller:
     The authors of RFCXXXX. (See section 8)


5.2 SDP usage of MPEG-4 Visual

   The MIME media type video/MP4V string is mapped to fields in the Session
   Description Protocol (SDP), RFC 2327, as follows:

   o The MIME type (video) goes in SDP "m=" as the media name.

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   o The MIME subtype (MP4V) goes in SDP "a=rtpmap" as the encoding name.

   o The optional parameter "rate" goes in "a=rtpmap" as the clock rate.

   o The optional parameter "profile-level-id" and "config" MAY go in the
   "a=fmtp" line to indicate the coder capability and configuration,
   respectively. These parameters are expressed as a MIME media type string,
   in the form of as a semicolon separated list of parameter=value pairs.

   The following are some examples of media representation in SDP:

   Simple Profile/Level 1, rate=90000(90KHz), "profile-level-id" and
   "config" are present in "a=fmtp" line:
     m=video 49170/2 RTP/AVP 98
     a=rtpmap:98 MP4V/90000
     a=fmtp:98 profile-level-id=1;
     config=000001B001000001B5090000010000000120008440FA282C2090A21F

   Core Profile/Level 2, rate=90000(90KHz), "profile-level-id" is present in
   "a=fmtp" line:
     m=video 49170/2 RTP/AVP 98
     a=rtpmap:98 MP4V/90000
     a=fmtp:98 profile-level-id=34

   Advance Real Time Simple Profile/Level 1, rate=25(25Hz), "profile-level-
   id" is present in "a=fmtp" line:
     m=video 49170/2 RTP/AVP 98
     a=rtpmap:98 MP4V/25
     a=fmtp:98 profile-level-id=145




5.3 MIME type registration of MPEG-4 Audio

   MIME media type name: audio

   MIME subtype name: MP4A

   Required parameters:
     rate: the rate parameter indicates the RTP time stamp clock rate. The
     default value is 90000. Other rates CAN be specified only if they are
     set to the same value as the audio sampling rate (number of samples
     per second).

   Optional parameters:
     profile-level-id: a decimal representation of MPEG-4 Audio Profile
     Level indication value defined in ISO/IEC 14496-1 [11]. This parameter
     indicates which MPEG-4 Audio tool subsets the decoder is capable of
     using.


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     object: a decimal representation of the MPEG-4 Audio Object Type value
     defined in ISO/IEC 14496-3 [5]. This parameter specifies the tool to
     be used by the coder. It CAN be used to limit the capability within
     the specified "profile-level-id".

     bitrate: the data rate for the audio bit stream.

     cpresent: this parameter indicates whether audio payload configuration
     data has been multiplexed into an RTP payload (See section 4.1 in this
     document).

     config: a hexadecimal representation of an octet string that expresses
     the audio payload configuration data "StreamMuxConfig", as defined in
     ISO/IEC 14496-3 [5]. Configuration data is mapped onto the octet
     string in an MSB-first basis. The first bit of the configuration data
     SHALL be located at the MSB of the first octet. In the last octet,
     zero-padding bits, if necessary, shall follow the configuration data.
     If the size of the configuration data is quite large, such large
     config data is RECOMMENDED to be indicated by in-band mode (cpresent
     is set to 1).

     ptime: RECOMMENDED duration of each packet in milliseconds.

   Published specification:
     Payload format specifications are described in this document. Encoding
     specifications are provided in ISO/IEC 14496-3 [3][5].

   Encoding considerations:
     This type is only defined for transfer via RTP.

   Security considerations:
     See Section 6 of RFCXXXX.

   Interoperability considerations:
     MPEG-4 Audio provides a large and rich set of tools for the coding of
     audio objects. For effective implementation of the standard, subsets of
     the MPEG-4 Audio tool sets similar to those used in MPEG-4 Visual have
     been provided (see section 5.1).

     The audio stream SHALL be compliant with the MPEG-4 Audio
     Profile@Level specified by the parameter "profile-level-id".
     Interoperability between a sender and a receiver may be achieved by
     specifying the parameter "profile-level-id" in MIME content, or by
     arranging in the capability exchange procedure to set this parameter
     mutually to the same value. Furthermore, the "object" parameter can be
     used to limit the capability within the specified Profile@Level in
     capability exchange.


   Applications which use this media type:
     Audio and video streaming and conferencing tools.


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   Additional information: none

   Personal & email address to contact for further information:
     See Section 8 of RFCXXXX.

   Intended usage: COMMON

   Author/Change controller:
     See Section 8 of RFCXXXX.


5.4 SDP usage of MPEG-4 Audio

   The MIME media type audio/MP4A string is mapped to fields in the Session
   Description Protocol (SDP), RFC 2327, as follows:

   o The MIME type (audio) goes in SDP "m=" as the media name.

   o The MIME subtype (MP4A) goes in SDP "a=rtpmap" as the encoding name.

   o The required parameter "rate" goes in "a=rtpmap" as the clock rate.

   o The optional parameter "ptime" goes in SDP "a=ptime" attribute.

   o The optional parameter "profile-level-id" goes in the "a=fmtp" line to
   indicate the coder capability. The "object" parameter goes in the
   "a=fmtp" attribute. The payload-format-specific parameters "bitrate",
   "cpresent" and "config" go in the "a=fmtp" line. If the string after
   "config=" is quite large, such large config data should not be
   transmitted by SDP but should be transmitted by in-band mode. These
   parameters are expressed as a MIME media type string, in the form of as a
   semicolon separated list of parameter=value pairs.

   The following are some examples of the media representation in SDP:

   For 6 kb/s CELP bitstreams (with an audio sampling rate of 8 kHz),
     m=audio 49230 RTP/AVP 96
     a=rtpmap:96 MP4A/8000
     a=fmtp:96 profile-level-id=9;object=8;cpresent=0;config=9128B1071070
     a=ptime:20

   For 64 kb/s AAC LC stereo bitstreams (with an audio sampling rate of 24
   kHz),
     m=audio 49230 RTP/AVP 96
     a=rtpmap:96 MP4A/24000
     a=fmtp:96 profile-level-id=1; bitrate=64000; cpresent=0;
     config=9122620000

   In the above two examples, audio configuration data is not multiplexed
   into the RTP payload and is described only in SDP. Furthermore, the
   "clock rate" is set to the audio sampling rate.

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RTP payload format for MPEG-4 Audio/Visual streams       February 2000



   If the clock rate has been set to its default value and it is necessary
   to obtain the audio sampling rate, this can be done by parsing the
   "config" parameter (see the following example).

     m=audio 49230 RTP/AVP 96
     a=rtpmap:96 MP4A/90000
     a=fmtp:96 object=8; cpresent=0; config=9128B1071070

   The following example shows that the audio configuration data appears in
   the RTP payload.

   m=audio 49230 RTP/AVP 96
   a=rtpmap:96 MP4A/90000
   a=fmtp:96 object=13; cpresent=1



6. Security Considerations

   RTP packets using the payload format defined in this specification are
   subject to the security considerations discussed in the RTP specification
   [8]. This implies that confidentiality of the media streams is achieved
   by encryption. Because the data compression used with this payload format
   is applied end-to-end, encryption may be performed on the compressed data
   so there is no conflict between the two operations.

   This payload type does not exhibit any significant non-uniformity in the
   receiver side computational complexity for packet processing  to cause a
   potential denial-of-service threat.


7. References


   1  Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9,
      RFC 2026, October 1996.

   2 ISO/IEC 14496-2:1999, "Information technology - Coding of audio-visual
      objects - Part2: Visual", December 1999.

   3 ISO/IEC 14496-3:1999, "Information technology - Coding of audio-visual
      objects - Part3: Audio", December 1999.

   4 ISO/IEC 14496-2:1999/FDAM1:2000, December 1999.

   5 ISO/IEC 14496-3:1999/FDAM1:2000, December 1999.

   6 ISO/IEC 14496-1:1999, "Information technology - Coding of audio-visual
      objects - Part1: Systems", December 1999.



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RTP payload format for MPEG-4 Audio/Visual streams       February 2000



   7  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997

   8 H. Schulzrinne, S. Casner, R. Frederick, V. Jacobson "RTP: A Transport
      Protocol for Real Time Applications",  RFC 1889, Internet Engineering
      Task Force, January 1996.

   9  ISO/IEC 14496-2/COR1, "Information technology - Coding of audio-visual
      objects - Part2: Visual, Technical corrigendum 1", March 2000.




8. Author's Addresses


   Yoshihiro Kikuchi
   Toshiba corporation
   1, Komukai Toshiba-cho, Saiwai-ku, Kawasaki, 212-8582, Japan
   Email: yoshihiro.kikuchi@toshiba.co.jp

   Yoshinori Matsui
   Matsushita Electric Industrial Co., LTD.
   1006, Kadoma, Kadoma-shi, Osaka, Japan
   Email: matsui@drl.mei.co.jp

   Toshiyuki Nomura
   NEC Corporation
   4-1-1,Miyazaki,Miyamae-ku,Kawasaki,JAPAN
   Email: t-nomura@ccm.cl.nec.co.jp

   Shigeru Fukunaga
   Oki Electric Industry Co., Ltd.
   1-2-27 Shiromi, Chuo-ku, Osaka 540-6025 Japan.
   Email: fukunaga444@oki.co.jp

   Hideaki Kimata
   Nippon Telegraph and Telephone Corporation
   1-1, Hikari-no-oka, Yokosuka-shi, Kanagawa, Japan
   Email: kimata@nttvdt.hil.ntt.co.jp












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